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Abstract

A model is developed that describes the power extraction in
chemical oxygen-iodine lasers (COIL’s) and CO2
gasdynamic lasers with stable resonators when a large number of
transverse Hermite–Gaussian eigenmodes oscillate. The extraction
efficiency, mode intensities, and intensity distribution along the flow
depend only on two parameters. The first is the ratio
γ0 of the residence time of the gas in the resonator to
the O2(1Δ) or
N2(v) energy extraction time and the second
is the ratio of the threshold to the small-signal gain. The
efficiency is maximum for γ0 → ∞ and decreases
rapidly as γ0 decreases. It is found that for a range
of parameters corresponding to the highest efficiencies the intensity
distribution along the flow is nonuniform and has two peaks near the
upstream and downstream sections of the resonator. In this case
only the highest-order modes that totally fill the resonator cross
section oscillate (the so-called, experimentally observed sugar
scooping bimodal intensity distribution). For the range of
parameters corresponding to smaller efficiencies the intensity is
uniform. In this case all the modes participate in lasing; however,
the intensities of the high-order modes are larger than those of the
low order. The current model is compared with the plane-mirror
Fabry–Perot resonator model and with the constant intraresonator
intensity and rooftop models of COIL’s with stable resonators. The
extraction efficiency calculated with the last two models is close to
that estimated from our model. However, the intensity distribution
cannot be calculated correctly using the Fabry–Perot, the constant
intraresonator intensity, or the rooftop model.

References

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